The invention relates to an apparatus for providing auxiliary power to a lighting unit for heavy equipment during interruptions of power from a direct current power supply.
Heavy equipment is often used in harsh environments characterized by severe temperatures, poor air quality, the handling of dangerous materials, among other conditions. For example, the large electromagnetic cranes that are used in a steel mill for handling ingot and containers of molten steel can be subjected to high temperatures, as well as sparks from the steel manufacturing process.
An exemplary electromagnetic crane 10 is depicted in FIG. 1. A crane is generally transported on rails 12 and 14 provided on the floor 16 or elevated above the floor of the steel mill. The rails 12 and 14 provide power from a direct current (DC) power supply 18 (e.g., a 250 volt DC (VDC) power supply) to a power bus 20 in the crane. The power bus 20 (e.g., a 250 VDC bus) is provided in one of the rails 12. The other rail 14 can provide the common or ground connection. The crane 10 has a horizontal section 26 which is provided with shoes 22 or other means that cooperate with the rails to guide the section 26 along the rails 12 and 14 and to prevent derailment of the crane. A section of the interior of the horizontal section 26 is illustrated to depict the contacts or brushes 24 provided on the crane for conducting a voltage provided via the power bus 20. Components on the crane that require power such as a luminaire 30, motors and control circuits are connected to the power bus 20. These types of cranes are generally only powered by a 250 VDC power supply 18 and therefore provide the only available power source for loads such as a luminaire 30. In addition, these cranes are typically not provided with uninterruptible power supplies (UPSs) because UPSs are regarded as too costly and not able to withstand the harsh conditions in which the cranes are used.
To ensure the safety of steel mill workers, many of the cranes used in the mill are automated or remotely controlled. Some cranes, however, can be manually operated by human operators located in a cab on the crane. Lighting is important to avoid mishandling of the steel, the crane and the various devices used during the manufacture of steel products (e.g., cauldrons for molten steel), particularly when the crane is manually operated by a human operator (i.e., controlled remotely or from within a cab on the crane). A number of existing cranes use either incandescent or high intensity discharge (HID) lamps which are subjected to intermittent power outages. For example, supply voltage to the crane can be interrupted by intermittent brush connections between the crane and the powered rails when the crane is in motion. In addition, electromagnets used on the crane to operate a boom, winch, grasping tool or other tool draw sufficient energy from the power bus to decrease, for varying periods of time, the system voltage provided to the crane by more than two-thirds. For example, the system voltage can decrease to 90 VDC or lower in a crane or other system using a 250 VDC power source. In the case of a conventional alternating current or AC-driven ballast, a voltage drop of this magnitude would cause the lamp to be extinguished. Direct current ballasts for HID lamps have been employed that have some degree of energy storage capability and can therefore withstand some interruptions in the supply voltage. These DC ballasts, however, are not able to prevent the lamp from being extinguished by the types of power interruptions that are common in the environments in which cranes and similar heavy equipment are used. While incandescent lamps do not cease operating as a result of voltage drop-off, they do not provide as much output and have a shorter operational life.
A need therefore exists for a device which provides a supply voltage to discharge lamps on heavy equipment when the supply of power between the heavy equipment and its power source is interrupted. A need also exists for a device which can supply a voltage to the heavy equipment lamps during power outages that does not require an auxiliary power source such as batteries or an AC power supply.
The above-described problems with lighting units for heavy equipment having only a DC power supply as a power source for the lighting units are overcome by the present invention.
In accordance with an aspect of the present invention, an energy storage bank is provided to ensure continued operation of the lighting unit during supply voltage drop-offs.
In accordance with another aspect of the present invention, a blocking rectifier is provided between the power supply and the energy storage bank to prevent bleedback to non-lighting loads in the power distribution system of the heavy equipment.
In accordance with yet another aspect of the present invention, the energy storage bank stores energy and provides the reserved energy to the ballast of a discharge lamp when the supply voltage to the ballast decreases below a level necessary for sustaining operation of the discharge lamp.
In accordance with still yet another aspect of the present invention, the energy storage bank comprises capacitors arranged in various series and parallel circuits.
In accordance with another aspect of the present invention, plurality energy storage banks can be arranged in parallel with respect to the ballast to increase the amount of power that is reserved to ensure continued operation of a discharge lamp following a sudden voltage drop-off.
A lighting system for machinery powered via a supply line connected to a direct current power supply is provided. The supply line provides a predetermined steady-state potential and the machinery is provided with a discharge lamp and ballast connected to the supply line. The lighting system comprises an energy storage bank connected in parallel with respect to the direct current power supply and the ballast. The energy storage bank comprises at least one capacitor and is operable to maintain a voltage across the ballast corresponding approximately to the steady-state potential of the supply line, and to discharge and provide an adequate voltage across the ballast to maintain operation of the lamp when power from the supply line to the ballast decreases below a selected voltage such as the rated voltage of a selected ballast.
In accordance with another aspect of the present invention, the selected voltage corresponds to a nominal operating voltage for the ballast to sustain operation of a gas discharge lamp.
A lighting system for machinery powered via a supply line connected to a direct current power supply is provided. The supply line provides a predetermined steady-state potential and the machinery is provided with a discharge lamp and ballast connected to the supply line and comprises non-lighting loads. The lighting system comprises an energy storage bank connected in parallel with respect to the direct current power supply and the ballast. The energy storage bank comprises at least one capacitor and is operable to maintain a voltage across the ballast corresponding approximately to the steady-state potential of the supply line, and to discharge and momentarily sustain a voltage across the ballast when power from said supply line to the ballast decreases below a rated voltage for a selected ballast. In addition, the lighting system comprises a bleedback device connected in series between the direct current power supply and the energy storage bank which is operable to prevent any of the non-lighting loads from draining power provided by the energy storage bank when power from the supply line to the ballast decreases below the rated voltage.